Moving image playback apparatus

ABSTRACT

A moving image playback apparatus capable of starting within a short time to play back reverse direction moving images is provided. The apparatus includes two decoders and one output buffer. In standby, using I-picture in a specified GOP as a reference, a controller causes a storage device to sequentially read first coded image data of the pictures in a first GOP preceding a specified GOP and the pictures up to I-picture in the specified GOP, and causes a first decoder to decode the first coded image data. Moreover, during the decoding of the first decoder, the controller causes the storage device to sequentially read second coded image data of the pictures in the specified GOP and the pictures up to I-picture in a second GOP following the specified GOP, and causes a second decoder to decode the second coded image data. Thereafter, the controller causes the outputs from the first and second decoders to be written to the output buffer. Thereby, the decoded image data are outputted from the output buffer immediately upon start of reverse playback, and moving images are played back.

FIELD OF THE INVENTION

The invention relates to a moving image playback apparatus applied to abroadcast program transmission system configured to store content to betransmitted as a broadcast program, for example. Particularly, theinvention relates to a moving image playback apparatus to allow checkingof content stored in a storage device by playing back the content in aforward direction or in a reverse direction.

BACKGROUND

The broadcast program transmission system is configured: to beforehandstore content to be transmitted as broadcast programs in a storageserver, and to play back and broadcast a specified content in accordancewith an instruction from an automatic program controller (APC). In theprogram transmission process, the content is usually checked inaccordance with the broadcasting sequence before the broadcasting.

In the checking of content to be broadcasted, an operator previews thecontent in forward playback, fast forward playback, reverse playback andskip playback while the content from the storage sever is sequentiallyread. A proposal was made on a method capable of smoothly acquiring areversely-played back image even when a preview is switched from aforward playback mode to a reverse playback mode (a patent document 1,for example).

Patent document 1: JP, P2006-303652A In content check, the moving imageplayback apparatus requires time to acquire a reversely-played backimage after switching from a standby mode to a reverse playback mode. Toput it specifically, since a B-picture is a bi-directionally predictivecoded picture in moving image data with an open GOP (group of pictures)structure, a B-picture preceding the I-picture cannot be decoded withoutthe image data in the immediately preceding GOP. For this reason, themoving image data needs to be sequentially decoded from the I-picture inthe immediately preceding GOP. When the moving image playback apparatusis in the standby mode at the I-picture in a particular GOP, the movingimage playback apparatus needs to read and decode the image data in theimmediately preceding GOP. Accordingly, the moving image playbackapparatus takes time to start a reverse playback and display areversely-played back image.

DISCLOSURE OF THE INVENTION Subject to be Solved by the Invention

The moving image playback apparatus has a problem of requiring time toacquire a reversely-played back image after switching from a standbystate. Accordingly, a method of reducing time needed to acquire areversely-played back image has been strongly desired.

An object of the invention is to provide a moving image playbackapparatus capable of starting within a short time to play back a movingimage in a reverse direction.

Means to Solve the Subject

To achieve the above object, a moving image playback apparatus accordingto the invention includes a storage device configured to beforehandstore moving image data with a GOP (Group of Pictures) structurecontaining an I-picture being an intra-coded picture, a P-picture beinga predictive picture produced based on the I-picture, and a B-pictureproduced based on the P-picture, a first decoder configured to decodethe coded image data read from the storage device and to output thedecoded image data, a second decoder configured to decode the codedimage data read from the storage device and to output the decoded imagedata, a selector configured to selectively output the image dataoutputted from the first decoder and the image data outputted from thesecond decoder, an output buffer configured to store and output theimage data outputted from the selector, and a controller configured tocontrol a read process performed by the storage device, decode processesperformed by the first decoder and the second decoder, and a switchprocess performed by the selector. Under a standby state, with theI-picture of a specified GOP used as a reference, the controller causesthe storage device to perform reading in which first coded image data ofpictures in a first GOP immediately preceding the specified GOP andpictures up to the I-picture in the specified GOP following the firstGOP are sequentially read from the storage device, and causes the firstdecoder to decode the first coded image data. Moreover, while the firstdecoder is decoding the first coded image data, the controller causesthe storage device to perform reading in which second coded image dataof pictures in the specified GOP and pictures up to the I-picture in asecond GOP following the specified GOP are sequentially read from thestorage device, and causes the second decoder to decode the second codedimage data. In addition, the controller causes the selector toalternately output the image data outputted from the first decoder andthe image data outputted from the second decoder by switching.Furthermore, upon start of any one of forward playback and reverseplayback, the controller causes the output buffer to output the imagedata.

In this configuration, the first and second decoders are used. Under thestandby state, with the I-picture of the specified GOP used as areference, the first coded image data of the pictures in the first GOPimmediately preceding the specified GOP and the pictures up to theI-picture in the specified GOP following the first GOP are sequentiallyread from the storage device, and are decoded by the first decoder. Inaddition, while the first decoder is decoding the first coded imagedata, the second coded image data of the pictures in the specified GOPand the pictures up to the I-picture in the second GOP following thespecified GOP are sequentially read from the storage device, and aredecoded by the second decoder. Thereafter, the image data decoded by thefirst decoder and the image data decoded by the second decoder arestored in the output buffer.

For this reason, when the reverse playback is started, the moving imageplayback apparatus is capable of outputting the moving images by justoutputting the decoded image data from the output buffer. Accordingly,the apparatus can make time needed to output the moving images afterstarting the reverse playback shorter than ever before. Furthermore,when the forward playback is started, the apparatus is capable ofquickly outputting the moving images without any delay due to thedecoding operation.

Effect of the Invention

The invention can provide a moving image playback apparatus which iscapable of playing back a moving image in a reverse direction within ashort time.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a moving imageplayback apparatus according to embodiment 1.

FIG. 2 is a diagram used to explain a playback operation of the movingimage playback apparatus according to embodiment 1.

FIG. 3 is a diagram used to explain a playback operation which themoving image playback apparatus according to embodiment 1 carries outwhen thinning images depending on a playback speed.

FIG. 4 is a block diagram showing a configuration of a moving imageplayback apparatus according to embodiment 2.

FIG. 5 is a diagram showing a GOP structure.

FIG. 6 is a diagram showing an order in which moving image data with aGOP structure is decoded.

EXPLANATION OF THE NUMERALS

-   -   11 Storage device    -   12 APC    -   13 First decoder    -   14 Second decoder    -   15 Selector    -   16 Output buffer    -   18 First output buffer    -   19 Second output buffer    -   17 Controller

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a moving picture playback apparatus according toEmbodiments of the invention will be described in detail with thereference to the drawings.

Embodiment 1

FIG. 1 is a block diagram showing a configuration of a moving imageplayback apparatus according to embodiment 1.

A storage device 11 beforehand stores content data (moving image data)for a broadcast program, and selectively reads the moving image data inaccordance with a broadcast instruction signal given to the storagedevice 11 by an APC (automatic program transmission controller) 12. Afirst decoder 13 and a second decoder 14 decode coded moving image datathus read, and output the decoded image data. The image data areinputted into a selector 15. Then, the selector 15 selectively storesthe image data in an output buffer 16. The image data stored in theoutput buffer 16 are outputted as moving image data from the outputbuffer 16 by a controller 17 when needed.

Furthermore, in accordance with an operation input instruction from anoperator, the controller 17 controls the read and write of coded imagedata from and to the storage device 11, the decoding of the coded imagedata by the first decoder 13 and the second decoder 14, the switching ofthe selector 15, and the read and write of the image data from and tothe output buffer 16.

Detailed descriptions will be herein below provided for various controlprocesses which are performed by the controller 17.

The moving image playback apparatus 1 causes an image data sequence witha GOP structure, which is read from the storage device 11, to beinputted into each of the first decoder 13 and the second decoder 14.

First of all, the GOP structure will be described using FIG. 5. The GOPstructure has three picture types of an I(intra)-picture, aP(predictive)-picture and a B(bi-directionally predictive)-picture. TheI-picture is intra-coded, the P-picture is forwardly predictive coded,and the B-picture is bi-directionally predictive coded. In other words,each GOP contains at least one I-picture being an intra-coded picture,P-pictures being predictive pictures produced based on the I-picture,and B-pictures produced based on the I-picture and the P-pictures. Thearrangement order in the GOP structure is IBBPBBPBBPBBPBB, and one GOPperiod is usually set up for 15 pictures, for example. When the GOPstructure is out of order, troubles such as image disturbance and imageinterruption occur during image playback. In addition, moving image datais recorded in the storage device in the above-mentioned arrangementorder, whereas, as shown in FIG. 6, the moving image data is decoded inthe order of BBIBBPBBPBBPBBP when the moving image is played back.

In moving image data with an open GOP structure, a B-picture precedingthe I-picture cannot be decoded without image data in the immediatelypreceding GOP, because the B-picture is a bi-directionally predictivecoded picture. Let us assume that, as shown in FIG. 6, the moving imageplayback apparatus is found in a standby state at I02-picture withinGOP2 by fast search. B00-picture or B01-picture in GOP2 cannot bedecoded without data of immediately preceding P14-picture in GOP1. Inorder to decode P14-picture, the pictures from I02-picture, whichprecedes P14-picture, have to be sequentially decoded. For this reason,a delay of approximately 0.5 seconds (equivalent to 15 pictures) occursbetween the start of the reverse playback and the display of B01picture.

FIG. 2 shows a relationship among coded image data to be decoded, thedecoders configured to decode the corresponding coded image data, andthe output buffer configured to store the decoded image data. As soon asthe moving image playback apparatus 1 according to the embodiment is inthe standby state, as shown in FIG. 2, the moving image playbackapparatus 1 decodes the coded image data of the pictures in the twosuccessive GOPs, and stores the decoded image data in the output buffer16. To put it specifically, the moving image playback apparatus 1actuates the first decoder 13 and the second decoder 14 at the sametime. Thereby, the apparatus 1 decodes the coded image data of thepictures in the preceding and following GOPs at the same time. By usingI02-picture in GOP2 being a standby position as a reference, thecontroller 17 causes the storage device 11 to read the coded image dataof the pictures in GOP1 (including B00-picture through P14-picture)preceding GOP2, as well as the coded image data of B00-picture,B01-picture and I02-picture in GOP2 following GOP1, from the storagedevice 11. Subsequently, the controller 17 causes the second decoder 14to decode the coded image data of the 15 pictures in one GOP period fromI01-picture in GOP1 through B01-picture in GOP2 which immediatelyprecedes I02-picture. In addition, while the second decoder 14 isdecoding the coded image data, the controller 17 causes the storagedevice 11 to read the coded image data of the pictures in GOP2(including B00-picture through P14-picture) inclusive of I02-picturebeing the standby position, as well as the coded image data ofB00-picture, B01-picture and I02-picture in GOP3 following GOP2, fromthe storage device 11. Thereafter, the controller 17 causes the firstdecoder 13 to decode the coded image data of the 15 pictures in one GOPperiod from I02-picture in GOP2 being the standby position throughB01-picture in GOP3 which immediately precedes I02-picture in GOP3.

B00-picture and B01-picture immediately preceding the first I-picture ineach GOP, are discarded, because B00-picture and B01-picture cannot bedecoded by the first decoder 13 or the second decoder 14. Afterward, thecontroller 17 causes the selector 15 to perform switching so that thedecoded image data of the I-picture and following pictures arealternately outputted from the first decoder 13 and the second decoder14 for each picture, and are then written into the output buffer 16.Note that the output buffer 16 is configured as a ring buffer. Here, thewrite pointer is set at a predetermined number for each picture and, asshown in FIG. 2, the output from the first decoder 13 and the outputfrom the second decoder 14 are stored in the output buffer 16 in a waythat, for each GOP, all the pictures contained in the GOP are stored inthe respective successive locations. In the ring buffer, each of thewrite pointer and read pointer move to the leftmost end upon reachingthe rightmost end.

If the write of the entire decoded image data to the output buffer 16 iscompleted, the image data are then outputted from the output buffer 16as soon as the reverse playback is started and the moving images areaccordingly played back. In addition, the image data are outputted fromthe output buffer 16 as soon as the forward playback is started, and themoving images are played back without any delay due to decoding.

Furthermore, once the playback is started, the controller 17 operates asfollows. In accordance with the playback direction of the currentlyoutputted GOP, the controller 17 causes the storage device to read theimage data of the pictures in the GOP following the currently outputtedGOP and the pictures up to the I-picture in the GOP following the GOPfollowing the currently outputted GOP from the storage device, as aunit. Then, the controller 17 causes the storage device to input thethus-read coded image data in the first decoder 13 and the seconddecoder 14 alternately. Subsequently, the controller 17 causes the firstdecoder 13 and the second decoder 14 to decode the inputted coded imagedata. Thereafter, for each 15 pictures in one GOP period from theI-picture in the GOP through a picture immediately preceding theI-picture in the following GOP, the controller 17 causes the selector 15and the output buffer 16 to alternately write the image data outputtedfrom the first decoder 13 and the image data outputted from the seconddecoder 14 to the output buffer 16 sequentially. Thereafter, thecontroller 17 causes the image data to be sequentially read from theoutput buffer 16, and then causes the moving images to be played back.

In a case where the forward or reverse playback is performed at 1.1 to1.9 times faster than the normal speed, as shown in FIG. 3, thecontroller 17 causes the first decoder 13 and the second decoder 14 torespectively thin output of the first decoder 13 and output of thesecond decoder 14 depending on the playback speed, and causes thethinned outputs to be written to the output buffer 16. When the decodedimage data are outputted from the output buffer 16 at the normal speed,the moving images are played back 1.1 to 1.9 times faster than thenormal speed.

The playback at a speed which is twice or more as fast as the normalspeed can be achieved through control of the first decoder 13 and thesecond decoder 14 by controller 17 in order that the first decoder 13and the second decoder 14 should decode only the I-pictures andP-pictures but no B-picture. The playback at a far faster speed can beachieved through control of the first decoder 13 and the second decoder14 by the controller 17 in order that the first decoder 13 and thesecond decoder 14 should decode only the I-pictures.

As described above, according to embodiment 1, the moving image playbackapparatus 1 uses the two decoders, that is to say, the first decoder 13and the second decoder 14. Under the standby state, with the I-picturein a specified GOP is used as a reference, the controller 17 causes thestorage device 11 to sequentially read first coded image data of thepictures in a GOP immediately preceding the specified GOP, as well asB00-picture, B01-picture and I02-picture in the specified GOP followingthe first GOP, from the storage device 11. Afterward, the controller 17causes the second decoder 14 to decode the thus-read first coded imagedata, and to write the decoded image data in one GOP period from theI-picture in the immediately preceding GOP through a picture immediatelypreceding the I-picture in the specified GOP to the output buffer 16. Inaddition, while the second decoder 14 is decoding the first coded imagedata, the controller 17 causes the storage device 11 to sequentiallyread second coded image data of the pictures in the specified GOP, aswell as B00-picture, B01-picture and I02-picture in the following GOP,from the storage device 11. Subsequently, the controller 17 causes thefirst decoder 13 to decode the thus-read second coded image data, and towrite the decoded image data in one GOP period from the I-pictureserving as the reference through a picture immediately preceding theI-picture in the following GOP to the output buffer 16.

Here, the coded image data in the two successive GOPs are decoded byusing the standby position as the reference. Accordingly, the movingimage playback apparatus can make the time needed to output movingimages after starting a reverse playback shorter than ever before at thestart of the reverse playback. Furthermore, the moving image playbackapparatus is capable of quickly outputting the moving images without anydelay due to the decoding operation, at the start of a forward playback.Moreover, for each two GOPs, the coded image data in the preceding GOPare decoded by one of the two decoders, and the coded image data in thefollowing GOP are decoded by the other of the two decoders. Accordingly,the moving image playback apparatus can make the time needed to decodethe coded image data shorter than ever before. In addition, theapparatus can play back the moving images quickly, even when theplayback mode is changed from the forward playback to the reverseplayback.

Embodiment 2

FIG. 4 is a block diagram showing a configuration of a moving imageplayback apparatus according to embodiment 2. Note that, in FIG. 4, thesame portions as those shown in FIG. 1 will be denoted by the samereference numeral, and detailed description for the portions will beomitted.

The moving image playback apparatus 1 according to Embodiment 2 isdifferent from the moving image playback apparatus according toEmbodiment 1 in that a first output buffer 18 and a second output buffer19 are provided to the output stages of the first decoder 13 and thesecond decoder 14, respectively.

The controller 17 causes the storage device 11 to read coded image datafrom the storage device 11, and causes the first decoder 13 and thesecond decoder 14 to decode the read coded image data. Subsequently, thedecoded image data outputted from the first decoder 13 are stored in thefirst output buffer 18, and are outputted depending on the necessity. Inaddition, the decoded image data outputted from the second decoder 14are stored in the second output buffer 19, and are outputted dependingon the necessity.

The image data stored in the first output buffer 18 or the image datastored in the second output buffer 19 are selectively outputted by theselector 15. Unlike the case of Embodiment 1, the switch operation ofthe selector 15 is controlled by the controller 17 for each GOP periodeven in the standby state.

Thereafter, if the write of the image data to the first output buffer 18and the second output buffer 19 are completed, the image data arequickly outputted from the first output buffer 18 or the second outputbuffer 19 as soon as the reverse playback is started, and the movingimages are accordingly played back. In addition, the image data areoutputted from the first output buffer 18 or the second output buffer 19as soon as the forward playback is started, and the moving images areaccordingly played back, without any delay due to the decoding.

Once the playback is started, each time image data become no longernecessary as a result of completion of output of the image data from oneof the two output buffers and the like, the coded image data of thepictures in the GOP next to the currently outputted GOP in the playbackdirection and the pictures up to the I-picture in the second next GOPare read from the storage device 11. The read coded image data aredecoded by the decoder connected to the output buffer storing the imagedata which become no longer necessary. Subsequently, decoded image datain one GOP period from the I-picture in the GOP through a pictureimmediately preceding the I-picture in the following GOP are overwrittento the output buffer. Thereafter, the output from the output buffer 18and the output from the output buffer 19 are switched for each GOPperiod, and the image data are sequentially read.

In the case of Embodiment 2, the decoded image data in one of twosuccessive GOPs are stored in the first output buffer, and the decodedimage data in the other of the two successive GOPs are stored in thesecond output buffer. For this reason, the moving image playbackapparatus is capable of making the time needed to output the movingimages after starting the reverse playback shorter than ever before atthe start of reverse playback as in case of Embodiment 1. In addition,the moving image playback apparatus can quickly output the moving imageswithout any delay due to the decoding at the start of forward playbackas well. Moreover, for each two GOPs, the coded image data in thepreceding GOP are decoded by one of the two decoders, and the codedimage data in the following GOP are decoded by the other of the twodecoders. Accordingly, the moving image playback apparatus can make thetime needed to decode coded image data shorter than ever before. Inaddition, the apparatus can play back the moving images quickly, evenwhen the playback mode is changed from the forward playback to thereverse playback.

Note that the invention is not limited to Embodiment 1 and Embodiment 2which have been described above. The invention can be carried out byvariously modifying the configuration of the moving image playbackapparatus, the sequence of the playback control within the scope of thegist of the invention.

INDUSTRIAL APPLICABILITY

The invention can make the time needed for a moving image playbackapparatus to output a moving image after starting a reverse playbackshorter than ever before, in a case where the reverse playback isstarted in a standby state. Accordingly, the invention can be applied toa moving image playback apparatus which is used for the purpose ofcarrying out forward playback, pause, and reverse playback repeatedly.

What is claimed is:
 1. A moving image playback apparatus comprising: astorage device configured to beforehand store coded image data with aGOP (Group of Pictures) structure containing an I-picture being anintra-coded picture, a P-picture being a predictive coded pictureproduced based on the I-picture, and a B-picture produced based on theP-picture; a first decoder configured to decode the coded image dataread from the storage device, and to output the decoded image data; asecond decoder configured to decode the coded image data, and to outputthe decoded image data; a first output buffer configured to store andoutput the image data outputted from the first decoder; a second outputbuffer configured to store and output the image data outputted from thesecond decoder; a selector configured to selectively output the outputfrom the first output buffer and the output from the second outputbuffer; and a controller configured to control a read process performedby the storage device, decode processes performed by the first decoderand the second decoder, and a switch process performed by the selector,wherein (a) under a standby state, with the I-picture of a specified GOPused as a reference, the controller causes the storage device to performreading in which first coded image data of pictures in a first GOPimmediately preceding the specified GOP and pictures up to the I-picturein the specified GOP following the first GOP are sequentially read fromthe storage device, and causes the first decoder to decode the firstcoded image data, and while the first decoder is decoding the firstcoded image data, the controller causes the storage device to performreading in which second coded image data of pictures in the specifiedGOP and pictures up to the I-picture in a second GOP following thespecified GOP are sequentially read from the storage device, and causesthe second decoder to decode the second coded image data; and (b) uponstart of any one of forward playback and reverse playback, thecontroller causes any one of the first output buffer and the secondoutput buffer to output the corresponding image data.
 2. The movingimage playback apparatus according to claim 1, wherein during any one ofthe forward playback and reverse playback: the controller causes thestorage device to perform reading in which coded image data of picturesin a GOP firstly following a GOP currently played back in the playbackdirection and pictures up to the I-picture in a GOP secondly followingthe GOP currently played back are read from the storage device, and toinput the coded image data read alternately into the first decoder andthe second decoder; the controller causes the first decoder and thesecond decoder to alternately decode the coded image data of thepictures in the GOP firstly following the GOP currently played back andthe pictures up to the I-picture in the GOP secondly following the GOPcurrently played back; and the controller causes the selector toalternately output the output from the first output buffer and theoutput from the second output buffer by switching every GOP period. 3.The moving image playback apparatus according to claim 1, wherein underthe standby state: the controller causes the first decoder to outputdecoded image data of pictures from the I-picture in the first GOP to apicture immediately preceding the I-picture in the specified GOP, out ofthe coded image data of the pictures in the first GOP and the picturesup to the I-picture in the specified GOP; and the controller causes thesecond decoder to output decoded image data of pictures from theI-picture in the specified GOP through a picture immediately precedingthe I-picture in the second GOP, out of the coded image data of thepictures in the specified GOP and the pictures up to the I-picture inthe second GOP.
 4. The moving image playback apparatus according toclaim 1, wherein at a certain playback speed, the controller causes thefirst decoder and the second decoder to thin out the correspondingdecoded image data, and to write the decoded image data thinned in thefirst output buffer and the second output buffer, respectively.
 5. Themoving image playback apparatus according to claim 4, wherein thecontroller causes the first decoder and the second decoder to decodeboth the I-picture and the P-picture, or only the I-picture depending ona playback speed.